Closed engine mount

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Fyre

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Hello, I am new to model rocketry, and this is my first post aswell. I have been designing 3d printed rocket parts, and I have a question about a triple engine mount design I had. I'll link the .stl file with the post, but to explain it, it is an engine mount that will fit into my fuselage and house my 3 a8-3 engines. In most other pre-made rocketry kits that I have seen, the other end of the rocket is exposed to the rest of the inside of the fuselage, with wadding to prevent it from burning the parachute. I was wondering if my design, which only has an opening on one side for the nozzle side, would have problems. If so, what can I do to solve this?
 

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How do you plan on deploying a parachute or streamer if your forward end is blocked?

Most black powder motors have an ejection charge and if you block the forward end of the motor mount the motor will eject out the back end of the rocket. This should usually be avoided, but some rockets are designed this way. However, they have a recovery system that will work anyway. The rocket may be very lightweight. It may use the ejection charge to snap the fins into a new position and the rocket helicopters down.
 
How do you plan on deploying a parachute or streamer if your forward end is blocked?

Most black powder motors have an ejection charge and if you block the forward end of the motor mount the motor will eject out the back end of the rocket. This should usually be avoided, but some rockets are designed this way. However, they have a recovery system that will work anyway. The rocket may be very lightweight. It may use the ejection charge to snap the fins into a new position and the rocket helicopters down.
Sorry, i'm really new to this and I cant find anything online about it. How do ejection charges work, I didn't know that the deployment of a parachute relied on it, to make the nosecone fall out and let the parachute loose. I just assumed that if I had my nosecone fairly loose, at the peak of its flight the nosecone could fall out.
 
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The ejection charge is a small amount of loose black powder. When the motor burns through the thrust and delay stages, the BP ignites and a puff of gasses causes an increase in pressure inside the rocket to eject the nosecone. The wadding serves to protect your streamer or parachute from the flame and hot gasses from the burning BP.
 
Ok, ill open up the mount so that the other end of the motor is open to the interior of the fuselage, but ill have a ridge that will stop the motor. Since there are 3 motors and 3 ejection charges, would the extra charges cause any problems? I'm probably just going to put 3x the normal amount of wadding to compensate but still.
 
The charges will probably not go off at the same time, but even if they do they will push the nose off and the parachute will come out. Use the normal amount of wadding for one, two or three motors. No extra is needed.

You want the nose to be on fairly tight. If it is loose it can come off during the boost phase and that is very bad. Your rocket can be badly damaged. The ejection charges will push the nose off. A good test is to hold the rocket by the nose and shake it a little. The nose should not come off. If it does, wrap some tape around the base of the nose cone and try again.

If your motor mounts are 3D printed they can warp due to the heat of the motors depending on what material you are using to print this. A friend of mine found that keeping the burnt motors in the rocket until they completely cool helps reduce distortion from the heat.

With three motors you will probably need nose weight to keep the rocket stable. A lot of weight in the rear needs to be offset by weight in the nose.
 
You want the nose to be on fairly tight. If it is loose it can come off during the boost phase and that is very bad. Your rocket can be badly damaged. The ejection charges will push the nose off. A good test is to hold the rocket by the nose and shake it a little. The nose should not come off. If it does, wrap some tape around the base of the nose cone and try again.
Hmm, I don't think I would ever use the words "fairly tight" when talking about nose cone fit for low-powered rockets. When adjusted to be "just tight enough" to keep the nose cone on, I would characterize it as still "fairly loose". LPR nose cones rarely come off during boost phase because they're too loose. However there have been many a lawn dart due to nose cones that are too tight.

(I realize that "fairly loose" and "fairly tight" are open to interpretation, just giving my own).

To the OP: Welcome to the hobby! Strongly suggest you go and read up on fundamentals of model rockets before continuing. Start here: https://www.nar.org/model-rocket-info/.
 
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To the OP: Welcome to the hobby! Strongly suggest you go and read up on fundamentals of model rockets before continuing. Start here: https://www.nar.org/model-rocket-info/.
After further thought I decided this needed more elaboration.

Your question suggests that you are really new to this. Nothing wrong with that, we all have to get started somewhere. However, designing a 3D-printed cluster is not what I would normally think of as a starter project. Personally, I like to recommend building at least a kit or two to get a feel for how to do things correctly and safely before going and designing your own stuff, and likewise you wouldn't normally build a cluster before you have some experience launching single-motor rockets. Sort of a crawl before walking before running approach.

But some other folks feel differently. So if you want to proceed , make sure you understand how to measure rocket stability, and can model your design in sim software such as OpenRocket. Also make sure you know best practices for lighting up clusters reliably, and the extra safety precautions required.

In general, be wary of adding much weight to the rear of the rocket. As Zeus-cat said above, clusters inherently have a lot of weight in back; a 3D-printed mount will add even more.

Good luck and please ask as many questions as you need to.
 
Welcome to model rocketry and to the forum.

My favorite line from movie Sully
“Can we get serious now?”



Your idea sounds cool, but you are running into problems immediately because apparently you don’t seem to have any significant Rocketry experience flying proven simple single engine manufacturer designed single motor kits and you want to START with a scratch built cluster rocket.

Your not gonna like this advice (and possibly less likely to FOLLOW IT) but buy, build, and fly a few simple rocket models. Even the little bitty ones are really a lot of fun, and you will learn from the experience. Get a new or used copy of Stine’s Handbook of Model Rocketry. It is actually an entertaining read, and trust me you will save far more money and time then it will take you to buy and read the book.

Take a hint from the experts, NASA. They didn’t launch a rocket two months after Kennedy’s speech putting Armstrong on the moon. They paced themselves with stepwise goals and got someone on the moon within the decade. Okay, yeah, the fact that they had a seemingly unlimited budget sure helped, but even WITH that, they didn’t build Rome in a day,

Your gonna sprain a lot of ankles (or worse) trying to learn to run before you can walk.

I wish you the best of luck, and remember if you aren’t having fun you aren’t doing it right!
 
I will also stress: Understand what the motor numbers mean.

Do you have a method of retaining the motors when their ejection charge fires?
 
Fyre,

Here is an internal diagram of the type of engine you want to use. You can see the ejection charge at the top of the engine.48C4458F-07EF-43CF-897D-23024751A1B6.jpeg

I agree with the overall sentiment of the others. You really should build a basic kit first to learn how these rockets work. Just from building a kit, you’ll learn about retention, ejection and that the nose cone doesn’t just separate on its own at apogee.

Also, you should read up on the science involved. In your case, especially stability. If you haven’t thought about it for your design, your rocket could end up going everywhere but straight. Three engines makes for a lot of weight at the wrong end. That could be dangerous.

We don’t want you to stop doing what you want to do. Just slow down a little and learn the basics first. Good luck.
 
I've built a few pre built model rockets and homemade ones, but for now I have a bunch of the weaker a8-3 engines and I wanted to get more power so I designed this. The pre built rockets never really explained how the landing system works, and I tried to google it but didn't really come up with anything, so I just assumed that it would fall off at apogee. Thanks for the input.
 
Hmm, I don't think I would ever use the words "fairly tight" when talking about nose cone fit for low-powered rockets...

Good point. I was in a hurry to respond as we had a launch today and I was running late (as usual). The OP said he thought the nose would fall off without any help and I was trying to go the other way with it.
 
I've built a few pre built model rockets and homemade ones, but for now I have a bunch of the weaker a8-3 engines and I wanted to get more power so I designed this. The pre built rockets never really explained how the landing system works, and I tried to google it but didn't really come up with anything, so I just assumed that it would fall off at apogee. Thanks for the input.
For the most part, from an efficiency standpoint in MODEL Rocketry, where the rockets are fin stabilized rather than having gimballed motors like NASA and Space-X, the best bang for your buck is going with larger motors, then probably clustering, and then multistage. Multistage on model rockets tends to be far less efficient than on gimballed rockets because you generally need more fin surface (and therefore more drag) and/or more nose weight (to counterbalance the center of pressure) to maintain stability, as increasing the number of motors in the tail puts more weight on the tai.

You’ve got a lot of room for power at your grasp by moving up to G motors before you require High Power Certification (and an FAA waiver launch site.)
 
I've built a few pre built model rockets and homemade ones, but for now I have a bunch of the weaker a8-3 engines and I wanted to get more power so I designed this. The pre built rockets never really explained how the landing system works, and I tried to google it but didn't really come up with anything, so I just assumed that it would fall off at apogee. Thanks for the input.
Yeah and yet you did not know about ejection charges. Go to Estes site and NAR site and read about model rocketry and Flight profile of a model rocket. Read the explanation of model rocket engine sizes. Go buy the Handbook on Model Rocketry. I am sorry but I read too many post where individuals art trying to do something before they are ready and do not really understand the basics yet.
 
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